Journal of Composite Materials

Single-walled carbon nanotube (SWCNT) reinforced titanium (Ti) matrix composites were produced by powder metallurgy (PM) and induction heating methods. It was found that nickel coating and a fast processing time associated with the induction heating method enabled nanotubes to survive the high-temperature (above 1950 K) processing conditions. The nanotubes were first covered with a nickel coating via the electroless plating method and then dispersed in the powder by ball milling. The powder was then cold pressed to make a PM preform which was melted by induction heating in an argon environment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations as well as Raman and X-ray Photoelectron Spectroscopy verification indicate that the nanotubes survived the high-temperature melting. Testing demonstrated that the hardness of the composites, which is directly related to strength, is improved with increasing weight percent of SWCNTs.

In order to improve the in situ oxidation kinetic condition of Al in copper matrix, Cr, instead of Al was in situ oxidized to form Cu/Cr₂O ₃ composites in the present investigation, Cu—Cr powders with different solubilities after mechanical activation were utilized to synthesize Cu/Cr₂O₃ composites, and their microstructure and stability were analyzed. The results show that although the Cu—Cr powders suffer from the same mechanical activation, Cr₂O₃ particles formed by the powders with different solubilities have great differences in size, amount, and distribution. In the range of experiments conducted, the Cu/Cr₂O₃ composite formed by Cu—Cr powders with 67% solution has large amounts of finer Cr₂O₃ particles uniformly distributed in the copper matrix and exhibited the best stability at elevated temperatures.

Composites made of polypropylene (PP) and wheat straw fiber treated by alkalization, acetylation, and maleic anhydride polypropylene (MAPP) were prepared, and the dynamic mechanical, thermal, and rheological properties of the treated composites have been investigated. The PP composites reinforced with the treated wheat straw fiber exhibited higher brittleness. The melt flow studies were carried out at the temperature of 170, 180, and 190°C and shear rate of 0.01—0.1 s^—1. The PP composites reinforced with the alkalized wheat straw fiber showed the high melt viscosity due to the strong chemical interaction among polymer and wheat straw fiber. The introduction of MAPP to the system increased the flow behavior of the polymer dispersed the wheat straw fiber uniformly, and decreased the melt viscosity. The PP composites introduced by 2 wt% MAPP showed the lowest storage flexural modulus (E^′) over the entire temperature range from 25—150°C, due to better compatibility between the wheat straw fiber and matrix. The PP composites made of with 20 wt% alkalized and MAPP treated wheat straw fiber showed the highest E^′. The differential scanning calorimeter (DSC) study revealed that introducing the wheat straw fiber to PP matrix increased the melting temperature and crystallization temperature. The PP composites reinforced with the alkalized and MAPP treated fiber had the highest rate of crystallization as a consequent of the co-effect of alkalization and esterfication.

Polypropylene/montmorillonite (iPP/MMT) has been investigated as an alternative to isotactic polypropylene (iPP) as a matrix for glass mat thermoplastic (GMT) composites. The melt viscosity increased significantly on MMT addition, but iPP/5.9 wt% MMT-based hybrid GMT preforms were fully impregnated after 30 s of compression molding, which is consistent with GMT industrial cycle times. The flexural modulus and strength increased monotonically with MMT content in consolidated hybrid GMT specimens prepared by compression molding, although the impact strength decreased. Moreover, the increases in the flexural modulus were greater than predicted from a conventional rule of mixtures taking into the measured Young’s moduli of the iPP/MMT matrices. Possible reasons for this are discussed.

New bimetal magnesium/aluminium macrocomposites containing millimeter-scale Al-based core reinforcement were fabricated using solidification processing followed by hot coextrusion. Two approaches were attempted for enhancing the performance of AZ31: (a) AZ31 shell integration with pure Al core (pure Al core approach) and (b) AZ31 shell integration with AA5052 core (AA5052 core approach), in that order. In the AA5052 core approach eventually, macrointerface width was increased by 2 orders of magnitude (compared to that in the macrocomposite obtained using the pure Al core approach), while stiffness was increased (+36%), 0.2%YS was unchanged and UTS was increased (+14%) (compared to monolithic AZ31). The evolution of the Mg-Al macrointerface and its effect on microstructure and mechanical properties is investigated in this article.

The bistability of unsymmetric cross-ply [0_n/90_n] _T laminates has already been investigated in much detail. In this work a new type of bistable laminate is presented which has a symmetric lay-up. Bistability derives from an unsymmetric fiber prestress applied to the laminate. The experimental procedure used to apply this fiber prestress is presented in detail. Experimental results are compared with analytical and finite element models which have the ability to model fiber prestress accurately. As well as having minimal hygrothermal variability, it is noted that the snap-through loads for a prestressed symmetric laminate can be much higher than its unstressed [0_n/90_n]_T equivalent.

Drilling carbon/epoxy laminates is a common operation in manufacturing and assembly. However, it is necessary to adapt the drilling operations to the drilling tools correctly to avoid the high risk of delamination. Delamination can severely affect the mechanical properties of the parts produced. Production of high quality holes with minimal damage is a key challenge. In this article, delamination caused in laminate plates by drilling is evaluated from radiographic images. To accomplish this goal, a novel solution based on an artificial neural network is employed in the analysis of the radiographic images.